It is already known to provide self-contained apparatus for surveying a physiological parameter or a group of parameters of a patient in the course of medical examination.
The examination using the principle known as nuclear magnetic resonance of the magnetic spins of hydrogen protons present in the tissues, requires the creation of an electromagnetic medium or environment in which is inserted the object or the subject to be examined.
Herein, and in the following text, the electromagnetic medium or environment is understood to mean the entire space in which the three necessary fields conjugate their effects in known manner to give the image of the explored region of the subject in the course of examination, namely:
the principal field which is a constant and homogeneous magnetic field of high intensity; PA1 the gradient, which is a magnetic field that varies as a function of space; PA1 the high frequency oscillating magnetic field in the radio frequency range. PA1 high frequency electromagnetic parasitic currents upsetting the action of the oscillating magnetic field. For this reason alone, all apparatus generating electromagnetic parasitic currents is prohibited in the shielded enclosure. PA1 deviations of the lines of force of the principal field outside the examination tunnel. These deviations arise from the presence of one or several ferromagnetic masses and are of such a nature as to modify the necessary uniformity of the principal field prevailing within the magnet. Care should accordingly be taken that the sum of the ferromagnetic masses present in the surveillance apparatus does not exceed a limit value which is a function of the distance which separates it from the superconductive magnet.
During examination, the patient is stretched out on a couch and introduced into the tunnel-shaped space a tunnel called an examination tunnel constituting the central region of a high powered magnet usually immersed in a cryogenic medium to render it superconductive. In this tunnel exists and is concentrated the electromagnetic environment needed for the examination.
So as not to disturb this electromagnetic environment, the magnet, its housing and all the nearby associated apparatus are disposed in an electrically shielded chamber, whose walls or partitions are of sheet copper assembled without electrical discontinuity, forming a Faraday cage. Then, the examination and control signals are filtered by several batteries of specific filters and analyzed by circuits disposed outside the chamber and then made visible in the form of an image by one or several screens on a console.
The disturbances engendered by a surveillance apparatus affecting the good operation of the NMR examining equipment can be classified in two distinct categories:
Conversely, the surveillance apparatus disposed adjacent the examination tunnel is subjected to disturbances due to the specific magnetic environment of the NMR imaging installation.
Thus, all apparatus whose operation is susceptible to being disturbed by the magnetic environment should not be used and requires important modifications and the adoption of protection. Of course, the use of any magnetic information supports or cathode ray tubes will be impossible.
Thus, no conventional complete information system can be useful, by reason of its mass memories and supports or various magnetic components.
Various adopted protections also cannot be dispensed with, because the central unit generates parasitic signals in the electric circuit.
Correspondingly, the control electronics of the display require high operating frequencies generating parasitic currents adapted to disturb the operation of the NMR imaging installation.
Thus, the proper operation of a surveillance apparatus adjacent an NMR imaging installation gives rise to numerous difficulties not yet solved at present.
A patient, such as an accident victim or premature baby placed in the examination tunnel, requires continuous surveillance by a doctor or qualified person, and the possibility of rapid intervention in the case of a physiological incident.
Furthermore, the straightness of the examination tunnel and its length adapted to accommodate the entire body, do not provide surveillance personnel with a sufficient field of vision to conveniently observe the patient in the course of examination.
Still further, the very high magnetic field in this region does not permit the use of any conventional assembly, for example surveillance optics using one or several video cameras.
It must of course be added, that this type of surveillance would not be sufficient to give information as to the condition of the patient and the immediate care needed by him in the case of momentary faintness.
Because of the impossibility of achieving even this minimum visual surveillance, the need for continuous automatic general surveillance assumes even greater importance.
Furthermore, a surveillance apparatus external to the insulating chamber, even if it were technically possible and operational, would not be of interest because of the pressing need for the surveillance personnel to be located beside the patient to intervene immediately in the case of fainting by the latter.
The surveillance doctor cannot enter into the shielded chamber in the course of examination under pain of rendering false the measurements, and it is out of the question, from a standpoint of cost, to devote two persons to this task.
Thus, this impossibility of suitably ensuring surveillance by an apparatus adjacent the NMR imaging examination equipment, not only does not square with the use of modern examination techniques, but constitutes a hardly permissible neglect in the case of patients who are frail or in a serious condition.
Also, the presence of a surveillance apparatus within the interior of the shielded chamber itself crowds the latter.
This important need, not yet satisfied at present, has been the subject of repeated efforts that are sustained and of great magnitude on the part of inventors to conceive and perfect automated surveillance functioning in a satisfactory manner adjacent the examination tunnel.
The present invention has for its object to operate a surveillance monitor in the shielded chamber and adjacent the superconductive magnet for medical imaging by nuclear magnetic resonance and thus to permit surveillance personnel to stay close to the patient and continuously have information on his condition.
Thus the surveillance apparatus according to the invention permits a person charged with surveillance and positioned beside the patient, simultaneously to know his condition and to be able to intervene immediately in case of faintness or difficulties.
The detailed technical characteristics and various other advantages are contained in the description which follows, given by way of non-limiting example with reference to the accompanying drawings, in which: